Start emacs with `emacs -Q`, press C-x C-f and type in a filename that
ends in .py like "foo.py". Then type in:

x = 3
rf"hello {x} world"

The whole string will be colored as a string literal. r means "raw" which
means no escape sequences and f means this is a format string where we can
interpolate variables like x. Delete the leading 'r' and the highlighting
will change so that {x} is not highlighted, since it's code. However, raw
and format strings are not mutually exclusive and it should be considered
code in both cases. If you run the snippet above in the interpreter you
will get "hello 3 world".

In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo
version 1.16.0, Xaw3d scroll bars)
 of 2021-05-14 built on eruv
Repository revision: efc24f1e0bb127481bcc9c3054c57c4cd3c99aa9
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12013000
System Description: Ubuntu 20.04.6 LTS